Questions tagged [density-functional-theory]

For questions about simulations using Density Functional Theory.

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Is it possible to build a force field that suits all elements based on vasp's machine learning result?

I have tried to use VASP's machine learning force field calculation during running molecular dynamics simulation with a supercell including some elements of Ti, O, Cu, etc. It does increase the speed ...
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Is the HOMO energy obtained from GW calculation always a value relative to the vacuum energy (-Ip)?

Aim: I want to obtain a reasonably accurate ionization energy (or work function in other terms) for a 2-dimensional hBN monolayer. The exact material does not matter much respective to the question, ...
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Coulomb energy in VASP

In DFT, the Coulomb energy is defined as the sum of Hartree energy, nuclear-electron attraction, and nuclear-nuclear repulsion. In VASP output, we can find the Hartree energy, and also the nuclear-...
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Academic help on the use DFT for modelling [closed]

I need help on the knowledge of DFT for semiconductor modelling/fabrications, from the scratch. I'm ready and willing to be your student please.
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Is there a system of multiple interacting quantum particles for which density can be obtained analytically?

I know that it is impossible for real electrons and nuclei. In the Kohn and Sham approach, a system of interacting electrons is approximated by a system of non-interacting Kohn-Sham particles in an ...
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2 answers
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Which formalism is better suited to model a crystal with defects: Hartree–Fock, Kohn–Sham, or something else?

Let’s suppose that (1) it’s required to calculate a crystal with certain parameters of a crystal lattice; (2) this crystal has some defects (let it be Frenkel defects for simplicity); (3) these ...
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What does it mean if the Fermi level crosses into the valence band? How about into the conduction band?

Just recently got into DFT and I've been doing a few calculations on my own on Quantum Espresso. I've come up with electronic band structures for materials that I've been looking at and I was hoping ...
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What is the best cell shape to calculate the energy of a free atom with a periodic DFT code (VASP)?

I want to study the adsorption energies of many different atoms to some surfaces. For that, I need to calculate the energies of free atoms (adsorbates) in a vacuum. I understand that I am supposed to ...
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1 answer
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Raman Spectra in Quantum Espresso

Does anyone have any experience simulating Raman spectra in Quantum ESPRESSO? Following the example 15 that comes with QE, I have attempted to simulate the Raman spectrum of MgO. I know the lraman ...
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Future and limitations of DFT

I'm a graduate student beginning research in condensed matter physics. Naturally, I am very interested in mathematics. I am aware that, in condensed matter physics, theorists employ tools from pure ...
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Successfully running parallel gas phase calculation on AMD cloud instance but implicit solvent fails (Local Intel workstation successfully runs both)

I am using an AMD Linux cloud-based instance to ran general optimisation and transition state calculations in parallel. I have noticed that I can run gas phase calculations in parallel but the run ...
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4 answers
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DFT code for simulating thousands of atoms in a supercell

I'm trying to simulate a supercell that contains thousands of atoms with the DFT method, but it seems VASP couldn't handle such a large system, its parallel efficiency is relatively low, when I try to ...
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density of state with spin orbit coupling

I have been doing DOS calculations with SOC tag on in VASP, and another calculation without SOC. As shown in the figure the DOS with SOC seems strange! is this wrong? How can I have resolved I have ...
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how to simulate the size effect with DFT theory?

I am considering simulating the size effect of nanoparticles, the size expands from 0.2nm to 50nm, but when trying to build the model, I am not sure how to reflect the size correctly, for example, if ...
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Predicting the band gap or some other properties of materials before running any calculations

Can we some how predict what sort of modulation will doping do to a material without actually running any calculations. Like perhaps we use the already known DOS of Zn in order to predict whether the ...
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1 answer
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Transiesta output through a single gold atom

I am looking for the electron transport study in a single gold atom, like the system of single carbon atom shown in transiesta paper by Nick Papior et al. Computer Physics Communications, 212, 8-24, (...
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How to save the generated 3d representation of the structure(s) by Viewer3d in Py4vasp?

I used py4vasp to calculate structure from data and then I displayed them in a structure viewer (Viewer3d) by this line: calc.structure[:].plot(). It returns a ...
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6 votes
1 answer
469 views

How to do simulation when two atoms exist in the same coordinate position in the lattice?

I found that there is a type of substance in which two atoms exist in the same coordinate position in the lattice, for example, FeF3(H2O)3, here is its crystal ...
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Effective mass of holes was measured using DFT

Effective mass of holes was measured using DFT. The hole value is different for each band, is there a way to get the average or standard value of this value? It was calculated using the VASP program. ...
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1 answer
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Why can't DFT calculate the accurate electronic configuration of the Oxygen atom?

I am trying to do a DFT calculation of Oxygen atoms with the VASP code. My settings follow the official tutorial on the Oxygen atom of VASP. But it turns out the energy levels of the two spin ...
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Why can't DFT calculate the energy of magnetic diatomic molecules accurately?

I am trying to calculate the reaction enthalpy change of $\ce{2H2 + O2->2H2O}$, my plan is to calculate the energy of $\ce{H2, O2 \text{and} H2O}$, respectively, then do the simple math. But I find ...
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How to estimate Photocurrent or Photo electron emission probability through Quantum espresso?

Or is there any Analytical methods available to estimate material response to incoming photon radiation.
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1 answer
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When is coupled cluster preferred over DFT?

I know that coupled cluster is considered to provide better accuracy than DFT, but I am not sure for which materials science applications or types of molecules that this higher accuracy is considered ...
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1 answer
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Simulating autoionization of small molecules using DFT or AIMD

From what I’m reading, simulation of autoionization in liquid substances is hard to do using gas phase DFT or AIMD[1][2][3]. I am using ORCA to do my work and I must confess that I’m shocked to see ...
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Scaling and speedup of Real-space based DFT calculations using Finite Elements approach

I have recently encountered paper where the authors have formulated Kohn-Sham equations using the finite-element package deal.II. It stated in paper DFT-FE was significantly faster than QE for all ...
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Are there any available tools to implement Jellium models?

I want to solve a Jellium-DFT like problem. Does any of the self-consistent/DFT software packages available allow to solve for the case of a Jellium configuration (no lattice)? If not I would like to ...
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14 votes
2 answers
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Textbooks for electronic structure theory

Through this post I am looking to create a resourceful list of textbooks for any one interested in electronic structure theory. The focus here is to create mostly a mutually exclusive list of answers ...
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7 votes
1 answer
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Analytic gradient and hessian for B3LYP

I'm studing DFT and I would like to know if there is an analytic expression for the first and second order derivatives of the PES obtained through the functional B3LYP. If so, I would need some ...
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Can you Calculate Magnetism at a Material's Surface?

I'm doing some research on FePt L10 nanoparticles, and I'd like to know how their surfaces affect their magnetic properties. However, I can't seem to find any papers on this topic. Specifically, I ...
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Decide the position of oxygen vacancy via the configuration with the lowest energy?

I am trying to determine the position of oxygen vacancy in $\ce{TiO2}$, is it reasonable to decide it by choosing the configuration with the lowest energy? It doesn't feel quite right to always choose ...
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2 votes
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Rashba effect and VASP

How to prove by first-principles DFT calculations that the compound has Strong spin-orbit coupling and Rashba effect
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Exchange potential for a non-interacting system

If I have a system of two "non-interacting electrons" and I want to mimic its density using another non-interacting system (KS system). Would the KS potential contain the exchange potential?
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band structure and primitive cell

When I use VASPKIT tool or SeeK-path to generate K-path file for a band structure calculation, it gives a PRIMCELL.vasp file , which has a unit cell that is ...
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Optimizing (DFT/MP2) small molecule dimers

I'm attempting to optimize n-alkane dimers using MP2/DFT in Gaussian09. However the first one or two frequencies are always negative. Can these modes be ignored or do I need to do a tighter ...
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6 votes
2 answers
521 views

Is there a closed-form sequence that mathematically converges to the exact exchange potential?

The Schrödinger equation, the fundamental basis of wavefunction-based methods, cannot be solved in closed form per se. One can, however, solve it by using a finite number of closed-form basis sets (...
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6 votes
1 answer
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For what DFT functional is useless to add D3 or similar corrections?

I would like to know for which DF is useless to add dispersion corrections. For example, I suppose that for the nonlocal density-based functionals such as wB97M-V it is unnecessary because the ...
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1 vote
1 answer
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Quantum Espresso calculation for Deuterium

I am a new user of Quantum Espresso. I have to use Deuterium instead of Hydrogen for my work in DFT studies. Hydrogen Pseudopotential file is available in QE website. Please clarify what parameters I ...
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5 votes
0 answers
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Getting Internal Calculator Data in ASE

I am using the framework ASE to do computational chemistry calculations. I am using the calculator GPAW with it. How do I extract data that is internal to the calculator? I mostly want to get the ...
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16 votes
2 answers
2k views

How to explain to a five year old why "DFT with local exchange–correlation functionals do(es) not describe van der Waals interactions accurately"?

From How do you explain Canada's Trudeau's power-sharing agreement to a five-year-old (American)?: The "explain to a five-year-old" question is a semi-standard format where the answer ...
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4 votes
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Compute solvation energies with (ESM) RISM-SCF

I want to use the 3D-RISM-SCF and ESM-RISM implementation in Quantum Espresso to compute solvated adsorption energies and absolute solvation energies. Before starting I read the main paper by S. ...
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1 vote
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Force convergence in Wannier orbitals based DFT code

I am working on Pt(111) / nanoparticles with various ligands, I am mainly using two softwares: A well known general purpose plane-wave code (Quantum Espresso). A less known software that is also ...
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6 votes
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Different band structure in supercell, but not due to band folding

This is my first time asking a question - if I mess something up please let me know and I'll amend. I believe this goes beyond questions on how to use QE so here seems appropriate over the QE forums. ...
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11 votes
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Calculating Core-Level Binding Energies (XPS) using DFT

I'm pretty new to DFT calculations but I'm trying to learn how XPS calculations are set up, particularly for open-shell molecular systems in common non-periodic DFT codes. A highly related secondary ...
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4 votes
0 answers
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RPA calculations with Hybrid Functionals

When doing RPA calculations as explained here, if I want to calculate it with hybrid PBE0 should I put LHFCALC = .TRUE. for just step 1 or step 1, step 3 and step 4?...
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9 votes
2 answers
255 views

Numerically integrating the Hartree potential

I'm trying to write a 1D density functional theory code on Python to predict the electronic structure of certain ions using the local density approximation. I'm trying to construct the hamiltonian for ...
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7 votes
1 answer
101 views

The relationship between average eigenvalue and convergence performance in VASP?

I meet some convergence problems when doing self-consistent field calculation in VASP, I find some parameters on VASP wiki that might be able to tune the convergence performance. But I don't quite ...
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1 vote
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can anyone please explain what is meaning of band.conf , mesh.conf and pdos.conf in phonon calculation?

Can anyone please explain, what is the physical meaning of band.conf, mesh.conf and pdos.conf in phonon calculation? if it is possible please explain about tags used in it.
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3 votes
0 answers
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How to select the projections and inner and outer window for wannier90 calculations?

I am new to wannier90 calculations. I am trying to obtain the wannier functions and wannier interpolated band structure. But I am having the problem in setting the parameters like ...
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14 votes
3 answers
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Can DFT simulate chemical reactions?

I was wondering, can you simulate the chemical reaction between two or more molecules using DFT? If not, what numerical method is usually used for this?
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10 votes
1 answer
129 views

How can the GGA functionals in libxc be evaluated?

For pedagogical reasons, I started adding libxc to the atomic DFT dftatom. In this program only spherical symmetric charges. That means that the final potential is just radial. To my understanding, if ...
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